In U.S. Pat. No. 4,143,639 to Frenette of Mar. 13, 1979 an elongated sealed casing, or inner drum is rotated on a vertical axis within an elongated sealed cylindrical casing, or outer drum at a clearance of about one eighth of an inch in the annular chamber formed within. A light lubricating oil normally occupies the lower portion of the annular chamber but rises to fill the chamber during rotation of the inner drum to frictionally heat the lubricant within the device.
The previously known patent has several important drawbacks which make it unsuitable for continuous operation of the device with the lubricating oil at high temperature.
This prior patent has no means for temporarily cooling the heated lubricating oil to a lower temperature within the device, but with continuous operation prolongs the period of time during which the lubricating oil is kept at the high temperature generated in the device, because the lubricating oil occupies the annular space within the outer drum and rotating inner drum and since the temperature of the lubricating oil is highest in this particular part of the device, a prolonged duration of time in this annular space for the lubricating oil causes oxidation and temperature breakdown to the lubricating oil.
Also in the previously known patent the lubricating oil used is a low viscosity oil (40 to 45 SSU at 210 degrees F.) such that; with continuous operation at high temperature (210 degrees F. to 260 degrees F.) as in a friction heater, oxidation and temperature breakdown of the lubricating oil will occur in a short period of time.